of some Phanerogamic Parasites. 3 1 7 
was collected in 1891 in the Botanic Garden at Bonn, and 
consisted of mature fruits, fruits from which the roots were 
just penetrating the cortex of the host, young two-leaved 
seedlings, and older stages of one and two years growth. 
The host was Crataegus monogyna , Jacq. 
The root from a germinating seed makes its way by solution 
and pressure through the cortex of its host into and through 
the phloem, and penetrates for a little distance into the 
young wood. The form of the haustorium thus imbedded 
is wedge-shaped, rather than conical. A tangential section 
of the host (a transverse section of the haustorium) shows 
that the young haustorium consists of two sharply defined 
regions, a cortex composed of rounded cells, rich in pro- 
toplasm, and with large spherical nuclei ; and a central 
region, elliptical in form, made up of more or less rectangular 
cells, those in the centre being thick-walled. A cross-section 
of the host (a radial section of the haustorium) shows that 
the cortex of the haustorium is composed of nearly isodia- 
metric parenchyma-cells with small intercellular spaces, that 
the cells at the periphery are thicker walled than those 
farther toward the centre, and that they abut against the 
somewhat compressed cells of the cortex and bast of the host ; 
that the central cylinder consists of tracheids in its centre, 
and of cambiform cells with large spindle-shaped nuclei 
surrounding these. No sieve-tubes are visible even when 
the tracheids have become numerous and thick-walled. 
In older plants, the haustorium sends through the cortex, 
parallel to and near the surface of the host, branches radiating 
in various directions and almost encircling the stem. A care- 
ful study of the main trunk of the haustorium (which in its 
mode of penetrating the host resembles a tap-root), and of 
its branches, shows only one structure that is not found 
in the younger stage. The tracheids are more numerous and 
unite directly, not at the tip, but at the sides of the hausto- 
rium, with the xylem of the host. Bordering the tracheids 
are the cambiform cells, with abundant protoplasmic contents 
and spindle-shaped nuclei ; but absolutely no sieve-tubes are 
